As I remember, 54 down Chevys had a strange arrangement of arms coming out of the side of the transmission. 55 up were much like all the later ones, and took a floor shift conversion much easier. I think places like JC Whitney carried some shifters for the early Chevys though, but I think they are now out of business. I'll do some internet snooping to see what I can find out for you.
I'm not sure. I just remember something about the 54 down transmissions being somehow different than the later ones. Might be in the mounting brackets or the arms. Every place I looked for an answer for creep I kept finding 55 on up shifters, except for that one place that had all early Chevy stuff. I would suggest creep call Hurst and Mr. Gasket to see if they make one for that car too.